Generally, a portable terminal refers to an apparatus carried by a user to execute a communication function with another user, such as voice communication, short text message transmission, or the like, a data communication function such as Internet, mobile banking, multimedia file transmission, or the like, and an entertainment function such as games, music, moving image reproduction, or the like. The portable terminal is generally specialized for a corresponding function such as a communication function, a game function, a multimedia function, an electronic note function, or the like, but recently, with the help of development of electric/electronic technologies and communication technologies, users can enjoy various functions merely with a mobile communication terminal.
As the mobile communication terminals have come into wide use, an effort has been continuously exerted to execute functions including control of vehicles, electric home appliances, etc., payment of transportation expenses, and a security function merely with the mobile communication terminal by mounting a wireless Local Area Network (LAN) or Near Field Communication (NFC) function on the mobile communication terminal, as well as a communication function through communication service operators. Therefore, the portable terminal represented by the mobile communication terminal needs to have various antenna devices mounted thereon. That is, a mobile communication service, a wireless LAN, and NFC are made in different frequency bands, such that respective antenna devices are required.
Moreover, as conversion to a fourth-generation (4G) communication scheme represented by wireless broadband (WiBro) or Long Term Evolution (LTE) has been made recently, super-high speed and broadband antenna devices are required. As such, a plurality of antenna devices are installed in a single portable terminal and at the same time, high-performance antenna devices are required. As a super-high speed and broadband antenna device, an Inverted F Antenna (IFA) or a flat-plate IFA is usefully used.
FIG. 1 is a perspective view schematically showing an antenna device 10 of a portable terminal according to an embodiment of the conventional art, in which the antenna device 10 is based on an IFA structure.
The antenna device 10 is structured by forming a radiation pattern 23 in a carrier 21 mounted on a circuit board 11. The radiation pattern 23 is properly designed according to a frequency band and radiation performance required by the portable terminal. On an end of the radiation pattern 23 is provided a shortcircuit pin 27 connected to a ground layer 13 and is also formed a feeding line 25 with a predetermined distance from the shortcircuit pin 27.
In this IFA structure, when the radiation pattern 23 is positioned on the ground layer 13, upon application of a transmission/reception signal to the radiation pattern 23, an induced current is generated on the ground layer 13 in an inverse direction to signal power flowing along the radiation pattern 23. The strength of the inverse current of the ground layer 13 increases as the signal power applied to the radiation pattern 23 is larger and a distance between the ground layer 13 and the radiation pattern 23 is shorter. The inverse current phenomenon degrades antenna performance, specifically, radiation efficiency, and therefore, to suppress the inverse current phenomenon, it is desirable to dispose the ground layer 13 and the radiation pattern 23 as far as possible from each other.
However, when the antenna device 10 is mounted in the portable terminal, increasing the distance between the ground layer 13 and the radiation pattern 23, i.e., a height H of the carrier 21 on the circuit board 11 hinders miniaturization of the portable terminal.
As an alternative for reducing the height of the carrier in the IFA structure, a fill cut region 15 is formed by partially removing the ground layer 13 on the circuit board 11, and the carrier 21 is disposed in the fill cut region 15. Through such a structure, the radiation pattern 23 is disposed in a position out of the ground layer 13 on the circuit board 11. By disposing the radiation pattern 23 in the fill cut region 15, the inverse current phenomenon is prevented, such that the radiation pattern 23 can be disposed closer to the circuit board 11. In other words, by forming the fill cut region 15, the thickness of the antenna device 10 can be reduced. However, it is substantially impossible to mount another part in the fill cut region 15 on the circuit board 11, such that the use efficiency of the circuit board 11 relative to the area of the circuit board 11 is degraded.
Eventually, the IFA structure, in spite of its super-high speed and broadband performance and usefulness in mounting on the portable terminal, is still an obstacle to miniaturization and slimmerization of the portable terminal.